[RESOLVED] Simple but fast weight system?

[adegans]

Hi all,

I need a weight system (or pointers/ideas for it) in PHP.

Currently i have a working piece of code and want to expand it with a weight system.
This code creates an array based on some conditions and variables.

array(0 => 2, 1 => 5, 2 => 10)

This array is flexible and can vary in length. Anything from 1 to many items.
The 2 5 and 10 are ID's of database records and can be different at any moment.

I've considered putting the weighting in the query but decided against it, otherwise i have to rewrite the rest of the system, which i don't fancy at this point. (unless it's the best most awesome way ofcourse)

I've found some examples, also on this forum, which create an array where items are listed multiple times in their array to increase their chance of being shown. This is no good because of a array_rand() later on which in some cases kicks in. I don't want the same item picked multiple times.

My idea is to create a 2nd array parallel to this one with weight numbers corresponding to those ideas and in some magical phpey way apply that to the existing method (above array) to sort that array by weight. That still leaves the randomizer as an uncertain factor but once i get some ideas/headstart i can figure that out i hope!

I have no code for the weight yet as i can't think of a way to do it 🙁

Any ideas, thoughts, comments welcome!!

Thanks!

[dagon]

something like this perhaps:

<?PHP

function pick_weight(){
	//keys match things to weight
	$things = array(
		'a','b','c','d','e');
	$weight = array(
		'1','10','4','3','1');

$sum_of_weight = array_sum($weight)-1;

$rnd = rand(0,$sum_of_weight);
foreach($things as $key => $var){
	if($rnd<$weight[$key]){
		return $things[$key];
	}
	$rnd  -= $weight[$key];
}
}

echo pick_weight();

?>

[adegans]

That looks about right 🙂

Gonna play with that in a bit. CHeers!

[adegans]

I've used the code, it works. But doesn't work with the array_rand() i use a little further down.
Also i bumped into a little issue where i in some cases need more values returned than just one.

I'll figure something out in that regard at a later stage.

Thanks!

[dagon]

you can call it multiple times to get multiple picks, for the other issue i would need to see your code to be able to help

[adegans]

I made some changes and this seems to work exactly how i need it to be:

//Construct an array(), irrelevant code stripped out in this snippet
foreach($linkmeta as $meta) {
	$selected[$meta->id] = $meta->weight;
	// Some array_diff items here
}

if(count($selected) > 0) {
	$banner_id = weight($selected);
	$output = ad($banner_id, false);
} else {
	$output = fallback($fallback, 'expired');
}

Allthough im not too sure about the math in your function:

function weight($ads) { 
    $rnd = mt_rand(0, array_sum($ads)-1);

foreach($ads as $key => $var) { 
    if($rnd < $var) return $key; 
    $rnd -= $var; 
} 
}

If i rotate 4 ads, 3 with weight 1 and one with weight 5 and refresh the page 40 times
I get 9 4 and 5 impressions on the 1 weight ones and 22 on the one with weight 5.

Maybe i'm not using your code properly but should a weight 5 not mean the ad is shown approx 5 times as often? Or how should i interpret it? (im horrible at such things so bear with me!)

[adegans]

Further testing shows i need a larger "cycle" of impressions to get more even stats.

I've settled on a 1 to 10 measure with options ranging 2 4 6 8 10, so 5 levels of "weight".

This seems to work best.
I've tested this repeatedly with runs of 400 page loads and comparing the results.

[adegans]

Additionally i sorted out the need for multiple returns with a for loop i already had and array_dif_key() the $selected array to prevent double ads being shown.

Same array format as for single selection. But after the result is used, strip that result from $selected to prevent it from being picked again.

for($i=0;$i<$block_count;$i++) {
	$banner_id = weight($selected);

$output .= ad($banner_id, false);

$selected = array_diff_key($selected, array($banner_id => 0));
}